Percorrer por autor "Alves, M. Rui"
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- Classification PDO olive oils on the basis of their sterol composition by multivariate analysisPublication . Alves, M. Rui; Cunha, Sara C.; Amaral, J.S.; Pereira, J.A.; Oliveira, BeatrizThe sterol compositions (GLC/FID/capillary column) of monovarietal olive oils (51 samples) from the most important cultivars of northeastern Portugal (Cvs. Cobranc¸osa, Madural and Verdeal Transmontana) and 27 commercial samples of olive oils with protected denomination of origin (PDO) from the same region and cultivars were evaluated. Δ-sitosterol, Δ5-avenasterol and campesterol were the most representative sterols. Cholesterol, stigmasterol, clerosterol and Δ7-stigmastenol were also found in all samples. All studied samples respected EC Regulation N. 2568, and in all cases total sterols were remarkably higher than the minimum limit set by legislation, ranging from 2003 to 2682 mg/kg. Results were analysed with the help of several statistical techniques, including reduction of dimensionality by principal component analysis with cross-validation of the number of components, followed by the use of canonical variate predictive biplots for model development and canonical variate interpolative biplots for approximate classification of monovarietal and PDO olive oils. These biplots proved to be a very interesting solution in the present case study, overcoming the problems of interpretation and classification that arise whenever different multivariate analyses are coupled together.
- Discrimination of varietal olive oils of the portuguese cultivars Cobrançosa, Madural and Verdeal based on their fatty acids compositionPublication . Oliveira, Beatriz; Pereira, J.A.; Casal, Susana; Alves, M. Rui
- Discrimination of varietal olive oils of the portuguese cultivars Cobrançosa, Madural and Verdeal based on their fatty acids compositionPublication . Pereira, J.A.; Oliveira, Beatriz; Casal, Susana; Alves, M. RuiThe fatty acid composition has been traditionally used to discriminate the different vegetable oils and confirm their authenticity. The aim of the present study was to check the possible use of the fatty acid profile to differentiate varietal olive oils of the three most important cultivars in Northeast Portugal (Cobrançosa, Madural and Verdeal). Fifteen varietal olive oils from each of the three cultivars were collected to achieve that goal. Fatty acids were determined, as methylesters, by HRGC. Methylesters were prepared by transesterefication with BF3/methanol after saponification with methanolic KOH. The fatty acid pattern was performed with a Chrompack CP9001 equipped with a split-splitless injector, a FID and a 50m x 0,25 mm i.d. fused silica capillary column coated with a 0.19µm film of CP-Sil88 (Chrompack). The temperatures of injector, detector and oven were 230, 250 and 185ºC, respectively. The results as shown by two-way Anova techniques and discriminant analysis demonstrate that C16:1c, C17:1, C18, C18:1c, C18:2cc and C18:3ccc can be used to discriminate the origin of each of the three olive oils.
- Effect of olive fruit fly infestation on the quality of olive oil from cultivars cobrançosa, madural and verdeal transmontanaPublication . Pereira, J.A.; Alves, M. Rui; Casal, Susana; Oliveira, BeatrizOlives (Olea europaea L.) from cultivars Cobrançosa, Madural and Verdeal Transmontana were collected separately and divided into two different groups according to the presence or absence of infestation by the olive fruit fly (Bactrocera oleae Gmel.). These two groups were then mixed in varying percentages to create five groups of olives per cultivar with infestation levels: 0, 12.5, 25, 50 and 100%. Each group was then processed to produce olive oil. The results, regarding mainly acidity, peroxide value, and stability to oxidation, suggest that olive fruit fly infestation reduces the quality of the olive oil. The effects of infestation varied according to cultivar, but in general the total tocopherol content was always lower at the 100% infestation level. The oil from cultivar Verdeal Transmontana had the lowest tocopherol content compared to oil from cultivars Cobrançosa and Madural, which could explain the lower quality of its oil.
- Influence of cultivar and environmental conditions on the triacylglycerol profile of hazelnut (Corylus avellana L.).Publication . Amaral, Joana S.; Cunha, Sara C.; Santos, Alberto; Alves, M. Rui; Seabra, Rosa M.; Oliveira, BeatrizThe oil of several hazelnut ( Corylus avellana L.) samples was extracted and evaluated for their triacylglycerol (TAG) composition. Trials were conducted in two Portuguese localities (Vila Real and Felgueiras) during three consecutive years and involved a total of 19 cultivars. The samples were analyzed by reversed-phase high-performance liquid chromatography with evaporative light-scattering detection. Sample preparation was fast and simple, consisting only of the dissolution of the oil in acetone, homogenization, and filtration, allowing this technique to be suitable for routine analyses. All samples presented a similar qualitative profile composed of eleven compounds: LLL, OLL, PLL, OOL, POL, PPL, OOO, POO, PPO, SOO and PSO (P, palmitoyl; S, stearoyl; O, oleoyl; and L, linoleoyl). The main components were OOO, LOO, and POO, reflecting the high content of oleic acid in hazelnut oils. A total of 79 different samples were studied, and the obtained data were statistically analyzed. Significant differences were verified in canonical variate plots when cultivars were grouped by country of origin. In general, the American cultivars were richer in TAGs with saturated fatty acids moieties, and the group of French, German, and English cultivars was richer in TAGs containing linoleic acid moieties. Differences were also significant when cultivars were grouped by year of production, showing that besides genetic factors, the TAG composition can be influenced by environmental factors.
- Influencing factors on bread-derived exposure to ochratoxin A: type, origin and compositionPublication . Duarte, S.C.; Bento, J.M.V.; Pena, A.; Lino, C.M.; Delerue-Matos, Cristina; Oliveira, Beatriz; Alves, M. Rui; Pereira, J.A.The nearly ubiquitous consumption of cereals all over the world renders them an important position in international nutrition, but concurrently allocates exposure to possible contained contaminants. Mycotoxins are natural food contaminants, difficult to predict, evade, and reduce, so it is important to establish the real contribution of each contaminated food product, with the aim to evaluate mycotoxin exposure. This was the key objective of this survey and analysis for ochratoxin A content on 274 samples of commercialized bread in the Portuguese market, during the winter 2007. Different bread products were analyzed through an HPLC-FD method, including traditional types, novel segments, and different grain based bread products. A wide-ranging low level contamination was observed in all regions and types of bread products analyzed, especially in the Porto and Coimbra regions, and in the maize and whole-grain or fiber-enriched bread. Nevertheless, the exposure through contaminated wheat bread continues to be the most significant, given its high consumption and dominance in relation to the other types of bread.
- Monitoring of ochratoxin a exposure of the Portuguese population through a nationwide urine survey – Winter 2007Publication . Duarte, S.C.; Bento, J.M.V.; Pena, A.; Lino, C.M.; Delerue-Matos, Cristina; Oliva-Teles, T.; Morais, S.; Correia, Manuela; Oliveira, Beatriz; Alves, M. Rui; Pereira, J.A.Ochratoxin A (OTA) is a mycotoxin produced by a variety of fungi, such as Penicillium verrucosum and Aspergillium spp., which has been found to have a wide number of potentially deadly toxic effects, and can enter the human organism through a variety of means. It then finds its way into the bloodstream and, after a lengthy process, is eventually excreted through the urine. It can thus be detected in its original form not only in blood samples but also in this biological medium. As such, and in an attempt to evaluate the exposure of the Portuguese population to this mycotoxin, morning urine samples were collected during the Winter of 2007, from each of five geographically distinct Portuguese locations — Bragança, Porto, Coimbra, Alentejo, and Algarve — and subjected to extraction by immunoaffinity columns and to OTA quantification through liquid chromatography coupled with fluorescence detection. Prevalent incidence was higher than 95% with Coimbra being the exception (incidence of 73.3%). In nearly all locations, the OTA content of most samples was found to be above the limit of quantification (LOQ) of 0.008 ng/ml. Indeed, excluding Coimbra, with an OTA content level of 0.014 ng/ml, all regions featured content values over 0.021 ng/ml.
- Tocopherols and tocotrienol content of hazelnut cultivars grown in PortugalPublication . Amaral, Joana S.; Casal, Susana; Alves, M. Rui; Seabra, Rosa M.; Oliveira, BeatrizThe effect of roasting on some nutritional characteristics of hazelnut lipidic fraction was investigated. Hazelnuts (Corylus avellana L.) were submitted to several different thermal treatments, comprising different temperatures (125-200 °C) and times of exposure (5, 15, and 30 min) and analyzed for their moisture and crude fat. Raw and roasted hazelnuts were also analyzed for their compositions in phytosterols and fatty acids (including trans isomers) by GC-FID, triacylglycerols by HPLC-ELSD, and tocopherols and tocotrienols by HPLC-DAD/fluorescence spectroscopy. Minor changes occurred in the fatty acid and triacylglycerol compositions. As temperatures and roasting periods increased, generally, a modest increase of oleic and saturated fatty acids and a decrease of linoleic acid, expressed as relative percentages, occurred. Similarly, an increase of triacylglycerols containing oleic acid moieties and a decrease of those containing linoleic acid moieties were found in the roasted samples. Roasting caused a modest decrease of the beneficial phytosterols (maximum 14.4%) and vitamin E homologues (maximum 10.0%) and a negligible increase of the trans fatty acids.
- Triacylglycerol composition of walnut (Juglans regia L.) cultivars: Characterization by HPLC-ELSD and chemometricsPublication . Amaral, Joana S.; Cunha, Sara C.; Alves, M. Rui; Pereira, J.A.; Seabra, Rosa M.; Oliveira, BeatrizA total of 26 walnut ( Juglans regia L.) samples from 9 cultivars (Arco, Franquette, Hartley, Lara, Marbot, Mayette, Mellanaise, Parisienne, and Rego) harvested in the 2001, 2002, and 2003 crop years and grown in two geographical origins (Bragancüa and Coimbra, Portugal) were evaluated with regard to their triacylglycerol composition. The methodology employed was reversed-phase highperformance liquid chromatography coupled to an evaporative light-scattering detector (RP-HPLCELSD) after extraction of the lipidic fraction of the nuts. Nine compounds were separated, identified, and quantified. All samples presented an identical qualitative profile composed by LLnLn, LLLn, LLL, OLLn, OLL, PLL, OOL, and PLO (P ) palmitoyl; O ) oleoyl; L ) linoleoyl; Ln ) linonenoyl). Trilinolein (LLL) was the major triglyceride, followed by dilinoeoyl-oleoyl-glycerol (OLL) and dilinoleoyl-linolenoylglycerol (LLLn), with mean values of 37.7, 18.5, and 18.4%, respectively. Significant differences in composition were found between cultivars, and these differences were also significant when cultivars were grouped by year of production, showing that besides genetic factors, the triacylglycerol composition can be strongly influenced by environmental factors.
- Vitamin E composition of walnuts (Juglans regia L.): A 3-year comparative study of different cultivars.Publication . Amaral, Joana S.; Alves, M. Rui; Seabra, Rosa M.; Oliveira, BeatrizThe tocopherol and tocotrienol composition of walnuts (Juglans regia L.) was determined for nine cultivars (cvs. Arco, Franquette, Hartley, Lara, Marbot, Mayette, Mellanaise, Parisienne, and Rego). Walnuts were harvested over three consecutive years from two different geographical origins (Bragancüa and Coimbra, Portugal), for a total of 26 samples. The methodology employed was a normal-phase high-performance liquid chromatography coupled to a series arrangement of a diode array detector followed by a fluorescence detector, allowing the simultaneous analysis of all tocopherols and tocotrienols. The analyses showed that all samples presented a similar qualitative profile composed of five compounds: R-tocopherol, â-tocopherol, ç-tocopherol, ä-tocopherol, and ç-tocotrienol. ç-Tocopherol was the major compound in all samples, ranging from 172.6 to 262.0 mg/kg, followed by R- and ä-tocopherols, ranging from 8.7 to 16.6 mg/kg and from 8.2 to 16.9 mg/kg, respectively. Multivariate analysis of the data obtained showed the existence of significant differences in composition among cultivars. These differences were also significant when cultivars were grouped by year of production, showing that besides genetic factors, the vitamin E composition was influenced by environmental factors.